Production of cured resin bodies by radiation pre-gelling and hot curing



United States Patent 3,246,054 PRODUCTION OF CURED RESIN BODIES BY RA-DIATHON PRE-GELLING AND HOT CURING John Richard Guenther, Mequon, Wis.,and Robert B.

This invention relates to the rapid and economical curing of resinousmaterials by combined radiation and heat treatment.

It is known to impregnate porous materials such as paper, cloth oforganic fibers, and glass filament fabrics with unsaturated polyesters;and effect a curing by heating in an oven, or by the employement ofgamma or beta radiation from various sources. For example, a paper web,impregnated with an unsaturated polyester mixture containing styrene,can be cured by heating for about ten minutes in passing through a120-foot oven, representing a production speed of about 12 feet of curedresin per minute. A beta-ray generator of the resonant transformer type,operating at one m.e.v (million electron volts) must deliver a dosage ofat least 8 megarads (eight million rads) .to effect a like cure; thisdosage being so large that commercially available beta-ray generators donot deliver the necessary power (in electrical watts) for curing ofcommercial widths at a satisfactorily rapid speed.

It has been found that a gelling or partial cure of such laminates canbe eifected by a radiation dosage of about one megarad; and that thecuring can then be effected rapidly in an air oven without theoccurrence of undesirable blistering effects such as occur whenoven-curing of a wet-laid stock is being conducted at high initialtemperataures for greater output.

An object of the invention is the production of a cured resin materialhaving a Barcol hardness value of 40 or over, by subjecting a liquidpolyestenstyrene resin mixture containing a peroxide curing catalyst, toa low intensity beta-radiation at a temperature not exceeding 'l30egrees F. whereby to eifect a rapid gelling, without blistering ordelamination, and thereafter heating rapidly to and at 250 to 300degrees for curing to a Barcol value of 40 or over.

Another object is the production of a coating or laminate having such amixture in cured form present therein and thereon, by impregnating aporous substrate with the liquid mixture, subjecting to the lowintensity radiation to effect gelling in situ, and thereafter rapidlycompleting the cure by heating to 250 to 300' degrees F.

A further object is the production of shaped articles by subjecting aporous substrate impregnated with such a liquid mixture to gelling by alow intensity beta-radiation, shaping to the desired form, and thencuring to a Barcol value of 40 or over by rapidly heating to and at 250to 300 degrees F.

EXAMPLE 1 A rigid general purpose polyester resin of intermediateviscosity was mixed in the proportion of 100 parts by weight with 8parts gy weight of styrene. In this example, the polyester -was a maleicanhydride and ethylene glycol condensate (the product availablecommercially under the trademark Pleogen-l300 being employed), andcommercial styrene was used as the solvent-additive. The liquid-resinblend had a sp. gr. of 1.14 with a weight ice of 9.54 lbs. per gallon;acid number 35; viscosity between 2,000 and 2,500 centiposes or Y-2 onthe Gardner-Holt scale; color below one. The permissable storage timewas found to be more than 6 months without harmful precondensation. TheS.P.I gel time was 3 to 4 minutes, the S.P.I cure time 5 to 6 minutes,and the S.P.I peak exotherm 400 to 410 degrees 35'. Before employmentfor impregnation, 1.0 percent by weight of tertiary butyl perbenzoatewas added as curing agent: the pot life was then found to be about fivedays at room temperature.

This mixture was employed to impregnate a decorated (so-called turquoiseconcerto) paper. The saturated material was exposed to one m.e.v. ofbeta-rays at 1.5 microamperes for a dosage of one megarad, whiletravelling at a linear speed of 30 feet per minute. The liquid resinmixture readily under-went gelation and formed a good gel. Upon removalfrom the radiation zone, it was exposed to air at 300 degrees F., andtherewith atttained a complete cure to a Barcol hardness of at least 40in seconds time: that is, the product is comparable to that by the aboveheat curing under commercial slow heat curing or by extensive radiationcuring. Comparably, when the uncured saturated web is brought into anair oven at 300 degrees F, pronounced blistering occurs: and hence, suchoven curing is commercially effected by gradually warming to the gelpoint, without exceeding 200 degrees F., and thereafter completing thecure at higher temperature, e.g., 300 degrees F.

The paper is illustrative of a porous substrate which will withstandheating to a temperature of 350 degrees F. while so impregnated, withoutdegradation by loss of strength or discloration: such substratesincluding paper, glass cloth, asbestos cloth and felt, cotton and linencloths, rayon cloths. Such substrates may be decorated with designs andornamentations before impregnation.

The tertiary butyl perbenzoatc is illustrative of a curing agent whichdecomposes at high temperature, but which does not shorten the pot lifeof the mixture at room temperature, or even up to degrees F., so greatlythat the contents of the impregnating vat must be consumed during asingle working shift: and thus permits the employment of theimpregnating mixture at a greatly reduced viscosity. During theradiation treatment, the peroxide appears to have no significant effectin the gelling: but it is energized during the later oven heating andproduces a hard resin rapidly.

By comparison, the dosages of beta radiation, with gelling beingproduced at one megarad, were 10 megarads to obtain Barcol hardnessreadings of 30 to 45; with a reading of at least 40 being that forcommercially acceptable complete curing. For these, the desirable cureswere at saturated web speeds of 10 feet per minute, and 8 to 10megarads: comparably, speeds of 20 feet or more per minute requireddosages beyond 10 megarads, the limit of the apparatus used. Industriallaminates on 15 mil glass cloth have been produced at 10 feet per minuteat one m.e.v. for a total dosage of 9 megarads, to produce a Barcolhardness value of 52, indicating a complete cure. 57 mil glass cloth and50 mil asbestos cloth, at two m.e.v. and a speed of 2 /2 to 5 feet perminute, with respective total dosages of 9 and 7 megarads gaverespective Barcol values of 52 and 57. A chlorinated polyester mixture(the commercially available Hetron- 32A being used) was gelled and fullycured under like dosages of 1 megarad and 9 megarads at like linespeeds; but discoloration appeared at dosages over 9 megarads in glassreinforced laminates.

The effects of amount of catalyst and line speed are indicated in:

7 made with a mixture of 100 parts by weight of the above ethyleneglycol; maleic anhydride resin, 10 parts by In Table I, Cat. indicatesthe catalyst and percentage by weight; with BPO being benzoyl peroxideand TBP being tertiary butyl perbenzoate. The line speed is stated infeet per minute. The Gel Point is given in megarads: each run being in asingle pass. The Oven Cure has the temperature (Temp) stated in degreesFahrenheit, and the time in minutes. Under Remarks, the abbreviationDelam. indicates that blistering occurred during the oven cure:therewith, Runs 7 and 8 show that the line speed should be reduced, andthe oven temperature reduced to 250 degrees F. or below with increasedoven time, to prevent blistering or delamination. Run 7 had a very lowand incomplete curing.

The reinforcing material and the impregnant exhibit reaction to theradiation, noting that the radiation delivers energy to the impregnantin effecting the gelling. The elfects of thickness and penetration canbe shown:

The abbreviations are as in Table I. All runs were with 1% TPB catalyst;with oven temperature of 250 degrees F. and time of 3 minutes. GelDosage is in megarads: in Run 11 even at 7 megarads, there was nogelation at the side opposite to that exposed to the radiation: in Run12, two passes at one megarad each were made: in Run 13, two passesformed at two megarads each were made, with no gelation'being at theopposite side. In Run 12, two glass cloths of and 50 mils were wet-laidin tandem. The one-sided exposure to a dosage of one megarad was noteffective with laminates of 80 mils or greater.

A like Run 14, using chlorinated polyester, styrene and 1 percent TBP,with 125 mil glass reinforcement, at a line speed of 10 feet per minuteand eight passes at 1 megarad each, gave a gelation at the exposed sidebut not at the other. After oven curing at 250 degrees F. for threeminutes, the exposed side showed a Barcol value of 40, but the oppositeside was essentially uncured.

The impregnation of reinforcement cloths and papers is facilitated bylow viscosity. The mixtures of polyester resin and styrene decrease inviscosity with increase of temperature: but conversely theprobability'of premature ouring increases with the temperature. Tests asto Resin Pot Life, that is, the time during which the mixture may beheld at impregnation temperature, were weight of commercial styrene, and1 part by weight of tertiary butyl perbenzoate, with the results:

Table III Penct. Cup Test. No. Temp. Vise. Pot Lite,

ays Initial Complete 77 580 20 Over 5 315 15 70 Over 4 240 11 55 180 845 2 165 7 40 135 6 30 105 5 20 1 Less than 24 hours. 1 Between 8 and 18hours.

In Table III, Red Scrim and Pearl Grey Decorative Papens, of commercialtype, were used. Temp. indicates temperature in degrees F. Visc.indicates viscosity (Brookfield) in centipoises. TPenet. Cup designatesthe standard cup test for penetration into the paper.

The procedure comprises the use of a low radiation treatment foreffecting a gelling and partial curing to not exceeding a Barcol valueof 10 at substantially room temperature and not exceeding 130 degreesF., and thus without the blistering and delamination which occurs duringa preliminary hot-gelling .at temperatures of 250 degrees F. or over, toproduce a gelled coherent and non-wet prod net; and a brief heattreatment at a temperature of 250 degrees F. or above, to eiTect acuring to a Barcol hardness of 40 or above.

The gelled material can be formed before the heat treatment: thus, itcan be shaped into three-dimensionally curved bodies and as partitionedtrays and receptacles, and then such shaped articles given the requiredhardness by the heat treatment. For example, food trays of the so-calledT.V. dinner type can be made, which can thereafter be heated to foodwarming or cooking temperatures without degradation of appearance; andsurface textures can be conferred upon laminate sheeting.

It is obvious that the invention is not restricted to the illustrativepractice, but may be employed in many ways within the scope of theappended claims.

What is claimed is:

1. A method of preparing a shaped article which comprises impregnating aporous substrate selected from the group consisting of paper, glass,asbestos, felt, cotton, linen, and rayon cloths with a liquid consistingessentially of a mixture of an unsaturated polyester resin, styrene andan effective amount of an organic-peroxide curing catalyst and exposingsaid impregnated substrate to about 1 megarad of beta-radiation whilemoving the impregnated substrate past the source of radiation at a rateranging up to about 30 feet per minute to obtain a partially-curedgelled impregnant having a Barcol hardness of about 10,,

then mechanically shaping said irradiated substrate and subsequentlyheating same at a temperature ranging from about 250300 F. for a periodof about 1 to 3 minutes to obtain the shaped article with the impregnanthaving a Barcol hardness of at least 40.

2. The method of claim 1 further characterized in that the curingcatalyst is present in an amount ranging up to about 1% by Weight of thepolyester and styrene mixture and is selected from the group consistingof benzoyl peroxide and tertiary butyl perbenzoate.

3. The method of claim 1 further characterized in that the polyesterresin is obtained from the reaction of ethylene glycol and maleicanhydride.

4. The method of claim 1 further characterized in that the liquidmixture consists essentially of 100 parts by Weight of the polyesterresin and 8 to 10 parts by weight of styrene.

5. The method of claim 1 further characterized in that the poroussubstrate is glass cloth.

6. The method of claim 1 further characterized in that the impregnatedsubstrate is exposed to about 1 megarad 5 of beta-radiation while movingthe impregnated substrate past the source of radiation at a rate rangingfrom about 10 to 30 feet per minute.

References Qited by the Examiner UNITED STATES PATENTS 2,959,531 11/1960Wheelock 204154 2,978,396 4/1961 Shewmaker et a1. 204l54 2,997,4198/1961 Lawton 204l54 SAMUEL H. BLECH, Primary Examiner.

MURRAY TILLMAN, Examiner.

1. A METHOD OF PREPARING A SHAPED ARTICLE WHICH COMPRISES IMPREGNATING APOROUS SUBSTRATE SELECTED FROM THE GROUP CONSISTING OF PAPER, GLASS,ASBESTOS, FELT, COTTON, LINEN, AND RAYON CLOTHS WITH A LIQUID CONSISTINGESSENTIALLY OF A MIXTURE OF AN UNSATURATED POLYESTER RESIN, STYRENE ANDAN EFFECTIVE AMOUNT OF AN ORGANIC-PEROXIDE CURING CATALYST AND EXPOSINGSAID IMPREGNATED SUBSTRATE TO ABOUT 1 MEGARAD OF BETA-RADIATION WHILEMOVING THE IMPREGNATED SUBSTRATE PAST THE SOURCE OF RADIATION AT A RATERANGING UP TO ABOUT 30 FEED PER MINUTE TO OBTAIN A PARTIALLY-CUREDGELLED IMPREGNANT HAVING A BARCOL HARDNESS OF ABOUT 10, THENMECHANICALLY SHAPING SAID IRRADIATED SUBSTRATE AND SUBSEQUENTLY HEATINGSAME AT A TEMPERATURE RANGING FROM ABOUT 250-300*F. FOR A PERIOD OFABOUT 1 TO 3 MINUTES TO OBTAIN THE SHAPED ARTICLE WITH THE IMPREGNANTHAVING A BARCOL HARDNESS OF AT LEAST 40.